The present invention relates to a navigational method for determining a route from a starting location to a destination location for a means of locomotion, especially for a motor vehicle, an airplane, or a ship, the route being calculated on the basis of a digital database, which includes predetermined path segments Wi having correspondingly assigned nodal points Ni, which connect individual path segments Wi to each other, specific weightings Gi being assigned to path segments Wi and/or nodal points Ni. The present invention also relates to a navigational system for determining a route from a starting location to a destination location for a means of locomotion, especially for a motor vehicle, an airplane, or a ship, a digital database being provided for calculating the route, the database including predetermined path segments Wi having correspondingly assigned nodal points N1, which connect individual path segments Wi to each other, specific weightings Gi being assigned to path segments Wi and/or nodal points Ni.
Navigational systems, such as those that operate on the basis of GPS (Global Positioning System), support an operator of a means of locomotion in navigating to a predetermined destination. In this context, the navigational system determines an optimal path, i.e., an optimal route, at least on the basis of starting and destination coordinates and of a corresponding digital database, which is essentially an image of the real street network and is also designated as a digital map. Conventional navigational systems calculate a route between two points taking into account previously defined average speeds, which are stored permanently for each street type that is present in the digital map. In any case, just as with PC-based route search programs, individual direction values can be defined by the user for the street classes, but these direction values often do not rest on true average values but rather on the assumptions of the user. Recently, it has become possible to adjust these speeds on the basis of the instantaneous traffic situation, which is termed xe2x80x9cdynamic navigation.xe2x80x9d However, these systems are cumbersome and expensive because they require a data connection from the navigational system to a telematic central office.
It is an object of the present invention to make available an improved navigational method of the type cited above as well as to make available an improved navigational system of the type cited above, which eliminate the aforementioned disadvantages. For this purpose, in a navigational method of the aforementioned type, it is provided in accordance with the present invention that weightings Gi that are used for the route calculation are varied in accordance with the time of day.
This has the advantage that the weighting of a street that is represented in a digital map is no longer constant but is viewed, or determined, as a function of time. In this way, by taking account of the fluctuations in the traffic density according to the time of day, more realistic data can be achieved for a calculated, anticipated duration of driving. In addition, the calculated route is adjusted to a specific time of day, because at the main traffic times, the main traffic routes are more significantly affected by a reduction in possible average speed than subsidiary routes.
For example, for each path segment Wi two weightings Gi are used for two times of day, or weightings Gi as a function of time t are determined as Gi(t).
In one preferred embodiment, weightings Gi are calculated from the product of Gi=Li*Ki, Li being a length of path segment Wi, and Ki being a path segment class that is proportional to the average speed that is possible on path segment Wi. To vary weightings Gi, path segment class Ki, which is assigned to this path segment Wi, is varied in accordance with the time of day.
A simple function for switching over between day and night conditions is achieved as a result of the fact that for each path segment Wi two path segment classes Ki for two times of day are used. This simple function has the advantage that the corresponding value only has to be calculated once before the beginning of the route calculation, and the route calculation then proceeds as if using a constant weighting. Alternatively, path segment class Ki as a function of time t is determined as Ki(t).
In a navigational system of the above-mentioned type, according to the present invention, variable weightings Gi are provided as a function of the time of day.
Thus, for example, for each path segment Wi two weightings Gi for two times a day are provided, or a predetermined function of time t is provided, which varies the weightings Gi as a function of time, yielding Gi(t).
In one preferred embodiment, weightings Gi correspond to the product of Gi=Li*Ki, Li being a length of path segment Wi, and Ki being a path segment class that is proportional to the average speed that is possible on path segment Wi. To vary weightings Gi, in this context, path segment classes Ki, which are assigned to this path segment Wi, are provided as a function of the time of day.
A simple function for switching over between day and night conditions is achieved as a result of the fact that for each path segment Wi two path segment classes Ki for two times of day are provided. This simple function has the advantage that the corresponding value only has to be calculated once before the beginning of the route calculation, and the route calculation then proceeds as if using a constant weighting. Alternatively, a predetermined function of time t is provided, which varies path segment class Ki as a function of time, yielding Ki(t).